Construction and maintenance of roads, especially secondary roads, requires a solid, stabilized base and sub-base on which to place the road surface. Preparation for road paving generally includes compaction of the base or sub-base, which may comprise clay, gravel, crushed stone, and the like, either taken from the native materials or transported to the site. Frequently, the base material includes crushed concrete and asphalt from the old road base or surface. Whether the material is primarily reclaimed from an old road surface material, taken from a new or old base on site, or is made from materials transported to the site, maximizing the stability of the material increases the longevity of the road surface and decreases the frequency and cost of repairs.
Soils too weak to bear the anticipated load can be stabilized by the addition of materials which impart mechanical strength, such as aggregate, and by the addition of chemical stabilizers, which decrease water absorption and increase the cohesion of the soil matrix by forming a cement-like compound to hold the matrix together. The appropriate type of stabilization and results to be expected depend upon the soil types encountered and methods of application of the stabilizer and construction of the road. A range of soil compositions can serve as good road base material, but high strength, resistance to shear, and resistance to erosion or swelling by water are required. Most native soils require some extent of stabilization to achieve these goals and provide a proper material for road construction.
Failure to provide an adequately stabilized base results in frequent and expensive repairs. Various techniques and compounds are known for stabilizing the soil or fill beneath pavement or other construction to provide a stable, high integrity base on which to place the pavement or other construction. Materials commonly used for this purpose include lime and fly-ash mixtures, calcium chloride, sodium silicates, mixtures of molasses and fuel oil, calcium acrylate, lignin sulfonate, and other materials.
Chlorides are the most commonly used product for soil stabilization. Calcium chloride assists in the compactive process, making it possible to obtain greater densities and greater strengths with normal compactive efforts. A major limitation of calcium chloride is its narrow application range. If the calcium chloride solution is applied at a less than specific dilution ratio the effectiveness of the compound is diminished, while application at a higher than necessitated dilution ratio causes beading on the application surface and thus prevents treatment of the target soil. Further, the widespread use of large quantities of chlorides has been shown to be environmentally harmful. Finally, chlorides are extremely corrosive on road construction and maintenance equipment.
Resins available under various commercial names are used as soil stabilizers and typically comprise lignin sulfonate, which is a by-product of the pulp milling industry. Lignin sulfonate is also referred to as “tree sap” by those skilled in the art of road construction. They provide cohesion to bind soil particles together, but are primarily used when they can be incorporated into the surface gravel.
Additives used for roadbed stabilization are disclosed by U.S. Pat. No. 4,106,296 (epoxy resins), U.S. Pat. No. 4,373,958 (lime kiln dust), U.S. Pat. No. 5,577,338 (fly ash), U.S. Pat. No. 5,820,302 (silicate and cement), and U.S. Pat. No. 6,689,204 (potassium formate and cationic polymer), all of which are incorporated herein by reference. U.S. Pat. No. 7,070,709, incorporated herein by reference, discloses various prior art compositions used for soil stabilization. Those products, however, have numerous disadvantages such as poor longevity, high cost, and environmental toxicity. The trade-offs are either accepting the environmental issues that come with products of longer useful life; dealing with a shorter lifespan for an environmentally friendly product; or paying significantly more for environmentally safe products with a favorable useful life.
A more acceptable method of roadbed stabilization is needed. It is an object of this invention to provide an improved composition and method of using the improved composition for soil stabilization that is both economical and environmentally sound.